Cinq has two pumps, one for front, one for rear, Sei has one pump.
Access is by removing the driver side front wheelarch liner, but we'll skip the forensics for now.
Most likely cause (we'll assume the pump mechanism is OK) is that the one way valve has gone down. These are hard little plastic valves plugged into the washer tube -- IIRC, the one for the front is near the bonnet stay. The system should work without, so, find and remove one way valve, bridge the gap with anything that's to hand. Test.
If it works, replace the one way valve at your leisure.
If not, come back.